Around 15 million years ago, the sea still made some temporary appearances in the area of today's Aiglun village, as shown by the tidal deposits found near this site.

The land gradually gained ground and the forest took hold. It is a deciduous forest (oaks, beeches, poplars, willows, etc.) crossed by numerous natural waterways that structured and shaped the sand deposits that have now become sandstone.

At that time, during the autumn periods, a multitude of leaves fell on these sands and were very quickly buried.

This rapid burial enables us today to find their fossilised prints. A few gastropods (snails) have also been found.